linux-kernel - RE: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed

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Date:   Wed, 15 Jan 2020 10:21:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'ira.weiny@...el.com'" <ira.weiny@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Dave Chinner" <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: RE: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed

>From ira.weiny@...el.com
> Sent: 10 January 2020 19:30
> 
> Page faults need to ensure the inode mode is correct and consistent with
> the vmf information at the time of the fault.  There is no easy way to
> ensure the vmf information is correct if a mode change is in progress.
> Furthermore, there is no good use case to require a mode change while
> the file is mmap'ed.
> 
> Track mmap's of the file and fail the mode change if the file is
> mmap'ed.

This seems wrong to me.
I presume the 'mode changes' are from things like 'chmod -w ...'.
mmap() should be no different to open().
Only the permissions set when the file is opened count.

Next you'll be stopping unlink() when a file is open :-)

	David

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